Low molecular weight polypropylenes are known (see Control Degradation of Polypropylene C. Tzoganakis, et al, Chemical Engineering Progress 84 (11), pp. 47-49, November, 1988). Low molecular weight polypropylene waxes are generally prepared from high molecular weight polypropylene by degradation. The degradation of high molecular weight polypropylene to produce low molecular weight polypropylene waxes are generally divided into two categories: thermal degradation and peroxide promoted degradation. High molecular weight polypropylenes having flow rates of 0.1 to 30 can be degraded thermally with a peroxide (known as controlled rheology) to produce lower molecular weight polypropylenes having higher flow rates (50 to 800 determined according to ASTM D1238-57T). Although the flow rates are higher than the starting flow rates, these polypropylenes are still plastic grade polypropylenes. Low molecular weight polypropylene waxes generally have flow rates much higher than 800 but are classified by Brookfield Thermocel Viscosity.
Flow rates of 0.1 to 30 generally correspond to molecular weights (number average) of 200,000 to 300,000 whereas flow rates of 50 to 800 correspond roughly to molecular weights of 80,000 to 100,000.
Propylene-ethylene copolymer waxes of low molecular weight (2000-6000 M.sub.n) having a ring and ball softening point of about 150.degree. C. are known. U.S. Pat. No. 4,988,598, discloses a toner composition for use in developing electrostatic images. The toner composition in this patent contains a thermoplastic styrene polymer, a coloring agent, and a low molecular weight propylene-ethylene copolymer wax. Low molecular weight propylene-ethylene copolymer wax can be prepared by thermal degradation of a high molecular weight propylene-ethylene copolymer without peroxide. However, low molecular weight homopolypropylene wax prepared by thermal degradation has a ring and ball softening point well above 155.degree. C. and does not provide adequate properties such as melt fixing temperature for toner applications. Additionally, the thermal degradation of homopolypropylene to produce low molecular weight homopolypropylene wax of lower ring and ball softening point results in low molecular weight homopolypropylene wax melt viscosities that are too low (below 30 cP at 190.degree. C.).
Although low molecular weight crystalline propylene-ethylene copolymer waxes of lower ring and ball softening point are known, it would, however, be very desirable to be able to produce low molecular weight crystalline homopolypropylene waxes having lower ring and ball softening points (RBSP) due to lower cost and convenience in manufacture.